This invention relates to a furnace viewing system, and particularly to an adapter which permits the use of a series of standard lens tubes with a variety of cameras, both black and white and color, vacuum tube and solid-state.
In a typical furnace viewing system, a commercially available wall box is installed in the wall of the furnace with its lens tube housing pointed toward the area to be viewed. For example, it may be desired to monitor the igniters and light-off, enabling continuous checking of flame patterns and verifications that all burners are operational. Monitoring can prevent damage to a boiler due to improper combustion, or downtime and maintenance due to a flame out. In some cases, the camera may be viewing a kiln or a molten pool of metal or glass.
If the furnace has a positive pressure with respect to ambient, the wall box is provided with a source of air to prevent the gases in the furnace from escaping through this opening. A lens tube is installed in and secured to the wall box, and attached to the lens tube is a camera contained within a housing designed to maintain the temperature of the camera within specified limits. The lens tube itself is also provided with means for maintaining the lens tube elements cool relative to the furnace.
In a typical installation, the lens tube is designed to image the interior of the furnace approximately one inch behind the end of the lens tube at a position where the light-sensitive element of the camera is located.
In a typical prior art black and white camera, the imaging element is a Vidicon tube. Usually, the tube is provided with means to provide for focus control. A Vidicon has a large dynamic range; it is not normally necessary to provide any variable physical control of the intensity of the light applied to the tube since that can be handled electronically once a proper fitter is selected. Also, the image formed by the lens tube is non-inverted, but this is not a problem with a Vidicon type tube since it would only be necessary to reverse the leads controlling the electronic scan of the target to provide the proper output to the monitor.
The use of color cameras allows the operator to view the flames in the furnace bed in their natural color, and quickly to observe any changes that might be occuring. However, present-day solid-state color cameras have a limited dynamic range, thus requiring an iris within the lens system to control the intensity of the light applied to the target, and most do not have any mechanism for controlling focus. Furthermore, the target is scanned electronically, and it is difficult without extensive modifications and redesign, electronically to invert the image that would normally be available from a standard or conventional lens tube.
One prior art attempt to correct the intensity, focus and image orientation problem resulted in the extensive redesign of the lens tube to add an iris for intensity control and additional lenses for inverting the image. This solution to the problem, however, was found to be unacceptable since it required the stocking of additional lens tube systems for use with color cameras. This results in a substantial increase in the cost of inventory for the modification of existing systems to color monitors.